According to Carrier Sensing Multiple Access/Collision Avoidance (CSMA/CA), which is a conventional multiple access method, transmission is performed when an idle channel is detected through carrier sensing, or when the channel is busy, transmission is postponed through backoff, which is revealed in the IEEE 802.15.4 Low-Rate WPANs Specification.
However, since the CSMA/CA method uses UWB impulse signals as short as less than several nanoseconds, the signal acquisition time taken for searching and determining accurate timing information of an impulse signal becomes long, compared to conventional systems using narrow band signals and when judging the presence of a signal, the probability of false alarm is high. Therefore, when the conventional CSMA/CA method is applied for multiple access in the ultra wideband impulse communication system, there is a problem that the performance of the CSMA/CA method is degraded remarkably.
Devices of a sensor network or a low-rate Wireless Personal Area Network (WPAN) should be designed to minimize power consumption when a communication scheme is designed because they are usually operated with small batteries. However, when the CSMA/CA method is used for multiple access in the ultra wideband (UWB) impulse communication system, the transmitting part of each device can begin transmission only when a channel is in an idle state. Thus, it should be in an active state while it monitors the channel. Also, since the receiving part of each device cannot know when the transmitting part begins transmission, it also has to remain in the active state while the channel is monitored. In short, since the transmitting and receiving parts of each device should remain in the active state while the channel is monitored, there is a problem of high power consumption.
Therefore, required are multiple access and communication methods that can minimize power consumption in the sensor network using UWB impulse communications or the low-rate WPAN environment and perform transmission and reception in a simple structure.
Since the sensor network can consist of more than hundreds to thousands devices, it is hard to support all the devices with the CSMA/CA technology which uses one channel. Therefore, a method for managing devices in a simple structure is needed.
Furthermore, since symbol-based Binary Exponential Backoff used in the conventional CSMA/CA method cannot relieve collisions between the devices, a hierarchical backoff method, which is an extended form of the symbol-based Binary Exponential Backoff, is required.
Compared to the conventional narrow band system using a band of several MHz, a band of 3.1 GHz to 10.6 GHz is split into bands of 500 MHz to bands of several GHz and each multi-piconet uses each split band in the ultra wideband impulse communication system. Thus, there is a problem that each sensor is too small to accommodate the transmitting and receiving parts having complicated functions to support bands of 500 MHz to bands of several GHz. This calls for the development of a method that can reduce the complexity in the transmitting and receiving structure and operate the multi-piconets in a simple method.
In addition, when an arbitrary time hopping pattern is determined and used between transmission and reception to apply an ultra wideband impulse signal to a time hopping system, it becomes more complicated to manage the time hopping pattern when there is a great deal of devices operated in the system. Therefore, a method that can simply manage the time hopping pattern in a simple manner is required.